First post here, so I apologize if I am breaking some conventions I am unaware of.
I am currently running a group of six people through Tomb of Annihilation
Spoiler Alert (follwing text may contain spoilers)
The campaign is decently well. The group of players is slightly rockier than what I'm used to, but all in all I'm fairly confident I can have all of my players enjoy themselves.
My problem is with one person.
My group of players is mostly a mish-mash of nationalities, so we play on Roll20, but two of them are real life friends of mine. One of those friends has always told me he enjoys the "game" part of D&D 5e more than the roleplaying, which is fair to me. Not everyone enjoys the same things about D&D and he happens to prefer the mechanics and such. He knows that I include a healthy portion of roleplay in my campaigns, but also like to provide challenging and interesting content that does not involve roleplay.
My first alarm bell should've rung when he purposefully made a mute character (An Aarakocra Monk) so he doesn't have to RP as much. I didn't think much of it at the time because his character communicated through writing and he had agreed with a different player to share a backstory. While this player indeed took a backseat to RP, he was still involved in the game. This has all changed over the course of the game. As time went on and everyone was chatting and having fun, he became more and more reclusive, simply not roleplaying and just being there to play. I have talked to him several times during this period but he assured me he was enjoying himself, so I left him be. This situation did get jarring when the character he shared a backstory with died and he did absolutely nothing in character to react to this.
As time went on, he also stopped talking less in our out-of-character conversations in addition to not roleplaying, limiting his interactions in the game to just making rolls when I called for it, declaring his attacks and asking if he could craft items during travel time. It was also at this point that he unlocked "Stunning Strike" as a monk, leaving him to use it constantly in order to get an advantage in combat. This is fine of course, but limited his interactions even further to just rolling his attacks and declaring he used Stunning Strike.
Finally, this situation came to a head when the party faced Tzindelor, a Young Red Dragon. The party was well prepared and had already done massive damage to her. This player came up and did Stunning Strike as many times as he could. Tzindelor passed most rolls, but critically failed one check, meaning she would be stunned and this epic battle everyone had in mind (it had only lasted a round or two at this point, her health was melting ridiculously quick) would've been reduced to the group just hitting a sandbag on HP. So at this point I made snap DM fiat decision and declared Tzindelor has Legendary Resistance.
Now we can all discuss on whether or not this was an appropriate thing to do (Please do make a side note in your reply if you want to, I am interested in other opinions), but the point is that this player was beyond frustrated about this.
Right after the event, he found the magical Greataxe in the dragon's hoard and refused to give it to the barbarian player in the group, despite the fact he can't effectively use it as his current character.
Other players asked in character if he wanted to give the axe to the barbarian (the other IRL friend) since he could actually use it. He did not respond and just said he wished to keep it out of character.
I did talk to him about this particular axe later, just asking why he wanted to keep it. He said something along the lines of him finally getting some loot. It's true he didn't get much in the way of magical items or upgrades, but then again there's only been two notable magic items in the group so far, an Alchemy Jug and the Ring of Winter. The Ring in particular is incredibly powerful, but I am slowly punishing the player for using it over time. (More details on how the ring ended up with the players can be provided on request). Eventually he did end up giving the axe to the barbarian because he was asked in real life by that character's player.
Finally, I've heard from a different GM from a different campaign that this player has been still bringing up this incident with the legendary resistance to him. Citing I am making him completely useless. While I can definitely understand the frustration at this particular instance, I have not stopped him from using Stunning Strike before and I genuinely believed the fight was more fun for it. I would happily offer some form of compensation, but I have no idea what to do since he doesn't roleplay and only spams Stunning Strike. I'll definitely let him wail on a boss sometime, but somehow I don't think that will really fix much (Confirmation bias is a pain).
I have invited this player for a talk, face to face, in the coming days. Can anybody offer advice on how to talk to this player? Suggestions for how to make him enjoy the game more would also be welcome. I will provide details as requested and provide an update after the conversation. Currently I am considering just asking him what he wants, what I could do to help. If we can't reach any solution, I might gently suggest this game might not be suited to his playing style and offer him the option of leaving. I'm not planning on telling him to leave. If he leaves, it will be because he agrees it's for the best.
I do genuinely hope to come to some sort of solution. The tension this has been causing has not only killed his enjoyment of the game, but is also affecting the atmosphere of the entire group, and nobody wants that.
Best Answer
Your "problem" player has already told you what they want, but the examples you relate suggest you may not be providing it.
As you say in the question, different people come to TTRPGs for different reasons. This particular player was pretty upfront with you: they don't like roleplaying very much, but do enjoy D&D's mechanics. This introduces a mild problem in that, when you provide RP sections of the game, they specifically aren't for this particular player, and they've taken steps to de-emphasize their very ability to participate in those sections.
Then comes the fight with Tzindelor. This player has built a character to interact with combat mechanics, which are apparently the only thing this player enjoys. Let's think about how things may have looked to this player:
Because their character's design (which you were fully aware of in advance of the fight) was too effective you changed the rules of the battle specifically to nerf them. This is worse than it may appear, because the fight was apparently already lopsided. The party had prepared well, and was dealing massive damage to the dragon right from the outset.
Bearing in mind that this player's only interest is in the mechanics of the game, this is a big deal-- their ability to plan for specific mechanics is shaken (the fundamental rules of the game and stats of enemies can change unpredictably at this table), and their work to play the game effectively in the one dimension they enjoy is self-defeating (if the character's build gains meaningful advantages, those advantages may simply be nullified, rendering the entire exercise in playing effectively worthless).
And it was only this player whose preparations were nerfed-- the rest of the party's preparations were rewarded via making the fight easier for them, apparently very easy. And the only time this nerfing happened was because the player's application of mechanics were "too good"-- had the dragon been modified to include Legendary Resistance prior to that game session, this would have been a very different situation.
What can be done, short of kicking this player from the group, one way or another?
1. Bring more mechanics into the non-combat portions of the game
Mechanics don't apply only during combat. There are endless opportunities for mechanical resolutions to any portion of the game. Instead of forcing this player to roleplay (which they don't like) or sit out of roleplaying situations (which reduces engagement overall), it's worth considering allowing this player to approach non-combat situations as dice rolls based off of their character sheet. This can also substitute for RP elements (with the player's agreement), like the character's lack of reaction to a significant backstory-related event-- they don't have to have an RP response for you to impose a mechanical penalty which represents the character's "appropriate" reaction to events.
I've done this in D&D and other game systems as well. If a player's character would be able to come up with a rousing speech, but the player can't think of something inspirational and captivating, well, we can roll the character's appropriate stats and leave the details to descriptive narration. If you provide enough information, and (potentially) a stable, rules-based system for "social combat" (or similar applications), then this player will have mechanics to work with in the rest of the game that isn't fighting. The player may or may not go for this approach, but it gives them an honest chance to participate in more of the game in their preferred mode.
2. Design combat scenarios to accommodate how your players play the game, and then let them play out
Because this character had access to Stunning Strike, and use of that ability was a dominant strategy against a single, high-threat opponent, the epic-ness of the battle was already in trouble. Making that ability arbitrarily useless is a fix for the problem, but one which is bound to disappoint.
If you instead build combat encounters in a way that can't be trivialized with Stunning Strike (or other abilities as they appear and cause issues), then the game changes. Some examples include multiple enemies, dangerous terrain that prevents the monk from sitting in range to use Stunning Strike, and clever battlefield designs that require (or reward) behaviors other than running up to an enemy and hitting it until it goes down. It's important that you provide opportunities for characters to shine using their hard-earned features and abilities, but you have more than enough freedom to design encounters such that those features and abilities aren't automatic wins for players.
Sometimes you'll be caught by surprise. If players come up with clever, effective strategies, they should enjoy the benefits of playing well. I know I've had boss fights rendered trivial because I failed to account for something my players cooked up.
Balancing combat challenges is difficult, but you have lots of options to modify fights fairly, adjust the campaign story to include more fights, or do anything else to make sure that players are challenged. Rewarding all players save one for their cleverness, then punishing that one player for their own cleverness by nullifying their clever idea alone, is bound to annoy.